This invention relates to a switching arrangement suitable for the ignition of at least one high-pressure discharge lamp by the production of ignition pulses. The switching arrangement is provided with at least three connection terminals, of which a first connection terminal is intended to be connected to a first terminal of the lamp and a second and a third connection terminal are suitable for connection on either side of an impedance connected in series with a second terminal of the lamp, and which is further provided with means for suppressing the production of ignition pulses if the lamp has ignited.
Such a switching arrangement is known under the type designation Philips SN 61 and is frequently used in practice, for example, in combination with a high-pressure sodium discharge lamp. The known starting arrangement is provided with an electronic circuit comprising a logic circuit, by means of which the production of pulses is blocked as soon as the voltage at an input of the logic circuit falls below an adjusted voltage level, which occurs as soon as the lamp ignites. In order to prevent the continued production of ignition pulses without interruption in the case of a defective lamp, the known switching arrangement is further provided with a counter circuit which blocks the production of ignition pulses after a preadjusted period of time. The production of ignition pulses is not activated until the supply voltage from which the switching arrangement is operated has been interrupted for some time.
The electronic circuit comprising the logic circuit, together with the counter circuit, forms part of the means for suppressing the production of ignition pulses if the lamp has ignited. A property of this known switching arrangement is that the production of ignition pulses remains blocked even if the lamp extinguishes without the supply voltage being interrupted. This means that when a lamp becomes defective during operation, the switching arrangement is not activated, which is a favourable aspect of the known switching arrangement.
In general a high-pressure lamp will already extinguish during operation when the applied supply voltage decreases in value for a short time without actually being interrupted. A decrease of 10% may already lead to extinguishing of the lamp. With the known switching arrangement, the lamp is not restarted under such conditions.